Process for improving the strength qualities of steel wire



Patented 0a. 22, 1929 UNITED STATES PATENT OFFICE WILHELM Ptl'NGEL, OF DORTMUND, GERMANY, ASSIGNOR TO THE I'IRM *VEREINIGTE STAHLWEBKE AKTIENGESELLSC'HAI'T, OF DUSSELDORF, GERMANY PROCESS FOR IMPROVING THE STRENGTH QUALITIES OF STEEL WIRE No Drawing. Application filed June 1, 1927, Serial No. 195,886, and in Germany June 4, 1926.

Whilst with drawn steel wire it is not very diflicult to obtain'a high tensile strength, the expansion, flexibility and torsional strength of such wire often do not meet practical requirements. Especially with hardened drawn steel vgire, as for instance transport rope wire and anchor strip wire, having a breaking strength of more than 200 kg. mmF, difliculties often arise, principally in respect to the expansion, the extent of which is of great importance especially for anchor strip wires in which expansion ratio is in most cases a very low one.

Now I have found that a considerable improvement of the strength of hardened drawn wires can be obtained by a short tempering treatment at about 350 centigrade. By this treatment a large increasing in the torsional strength and also of the expansion is obtained, whereas the breaking strength will be only slightl decreased, if temperature and duration 0 tempering are suitably chosen. 1; is, however, possible to take into consideration this slight lowering in the tensile strength during the drawing operation. Even wires having low torsional strength in consequence of an unsuitable manner of drawing can be strengthened bythe process according to the invention. a

The new process is carried out in such a manner that a thermal treatment at about 350 Centigrade is provided for after the last cold drawing, which' fiis preferably eflected in soap. The proper temperature and the duration of tempering must be chosen in each case according to the kind of material to be treated and to the value of strength desired to be obtained, care being taken that the temperature of the Ac point is not exceeded, in new of the fact that above this point tem pering is no longer possible, because thoroughannealing is then taking place with the result that the substantial c aracteristics of cold working disappear. The thermaltreatment may be either effected in such a manner that the wirc'is drawn through a leador salt-bath heatedju'p to about 350 centigrade at a suitable speed,'orit may be carried out by tempering the wire rolled into rings in a furnace,

orinstance in an annealing box or the like.

Wires which have to be galvanized, tinned or subjected to any other further treatment after the last cold drawing, are subjected to the thermal treatment according to the invention before this further treatment.

What I claim and desire to secure ters Patent of the United States is 1. Process .for improving the mechanical strength of steel wire in such a manner that the capacity for expansion increases considerably while the tensile qualities undergo comably while the tensile qualities undergo comparatively little change comprising subjecting the wire after the last cold drawing to a temperature of at least 350 C. but not higher than the Ac point during such a short time that the state of equilibrium in respect to the general strength qualities is not reached.

WILHELM PUNGEL.

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